1. Field of the Invention
This method relates generally to gaskets for establishing a gas and fluid-tight seal between two members such as exhaust components of an exhaust system for an internal combustion engine or for turbo charger joints of an internal combustion engine.
2. Related Art
Many gaskets for establishing a gas and fluid-tight seal between exhaust joints in an internal combustion engine are made of ASTM A666, Type 301 full hard stainless steel (hereinafter referred to as the “Type 301 Alloy”). Type 301 Alloy steel has a composition which includes, by weight percentage: up to 0.75% Silicon, up to 2.00% Manganese, up to 0.045% Phosphorus, up to 0.030% Sulfur, 16.00-18.00% Chromium, 6.00-8.00% Nickel, up to 0.10% Nitrogen, up to 0.15% Carbon and the remainder of Iron.
Such gaskets are typically formed from sheet of cold rolled material. During the cold rolling process, martensite is formed into the Type 301 Alloy steel material, which provides the resulting gasket with excellent mechanical properties for use as an exhaust gasket. However, in order to increase fuel efficiency, advanced technologies, such as direct injection and turbocharging, are increasingly being used in internal combustion engines. Such technologies result in increased combustion and exhaust temperatures. This may be problematic for exhaust gaskets made of Type 301 Alloy steel because, at temperatures above 430° C., some of the martensite may convert to a comparatively weaker austenite phase, thus reducing the strength of the exhaust gasket and diminishing its sealing abilities. This strength is not recovered after cooling, thereby permanently weakening the gasket.